The present invention relates to a method and apparatus for switching a satellite receiver between two operating modes depending on whether the receiver is stationary or mobile.
Satellite digital audio radio service (SDARS), a satellite broadcast service established by the U.S. Federal Communications Commission (FCC), has been proposed using satellite transmission of digital audio programs to radio receivers. The radio receivers can be stationary receivers, in which case a receiver antenna can be pointed for optimal line of sight (LOS) reception from a satellite. In contrast, the position of the receiver antenna relative to the satellite changes with mobile receivers (e.g., a receiver that is hand-carried by a user or is mounted in a vehicle), and LOS reception from one satellite is not always available. Accordingly, mobile receivers are generally configured to receive broadcast signals from more than one satellite.
Service outages can occur in systems which broadcast data, video, audio and other information using radio frequencies. These outages can prevent receivers, and particularly mobile receivers, from receiving the broadcast service altogether, or cause them to receive a signal so degraded that the service is rendered unacceptable. These outages are generally due to physical blockage of transmission paths between the transmitter and receiver (e.g., due to mountainous terrain or long tunnels) and multipath fading and reflection of the transmission path. Satellite broadcast systems can use two transmission channels to provide diversity for mitigating service outages due to multipath, physical blockages and interference in mobile broadcast receivers. Terrestrial repeaters can also be provided to repeat satellite signals in geographic areas where LOS reception is obscured by tall buildings, hills and other obstructions.
The receivers are configured with first and second receiver arms for receiving signals transmitted from the respective satellites. The recovered data streams from the satellites can be used singly or optimally combined. In satellite systems that are reinforced with terrestrial repeaters, the receiver can also be configured for dual-mode operation to receive both satellite signals and terrestrial signals and to combine or select one of the signals as the receiver output. When the receiver is stationary, only one of the satellite signals is generally required. When the receiver is in a mobile environment, the option of using one or plural received satellite signals for output signal generation is advantageous, particularly when no terrestrial repeater signal is available.
In accordance with the present invention, a satellite receiver is switchable between an operating mode wherein the receiver is capable of generating an output signal using received signals from one or a plurality of satellites, and another operating mode wherein the receiver generates an output signal using signals received from only one satellite. The former operating mode is useful when the receiver is operating in a mobile environment (i.e., installed in a vehicle). The latter operating mode is useful when the receiver is operating in a fixed environment (e.g., installed at a user""s home or otherwise operated at a stationary position).
In accordance with another aspect of the present invention, the receiver is configured to detect the mode (i.e., fixed or mobile) in which it is operating. The receiver comprises at least two receiver circuit arms. Each arm is configured for receiving, downconverting and demodulating a broadcast signal from a selected one of the satellites. The receiver is operable to disable at least a portion of one of the two arms when the receiver operating mode corresponding to fixed or stationary use is detected.
The mobile or fixed mode can be detected depending on whether the receiver is powered on via a DC power supply (e.g., 12 volts or greater from a vehicle battery via the cigarette lighter receptacle or power receptacle) or a residential power supply circuit (e.g., AC power or DC power of 9 volts), respectively. A circuit is provided to detect the signal level from the power source and operate a relay which selectively enables and disables components in respective receiver arms.
The mode can be detected depending on the position of a switch operated by a user. The receiver can also be operated in conjunction with a pedestal base which actuates a switch or detector in the receiver. The pedestal base is installed in a vehicle (e.g., on the dashboard of the vehicle). The switch or detector is actuated when the portable receiver is placed on the pedestal.
In accordance with yet another aspect of the present invention, the receiver is provided with a power supply sensor for determining if the receiver is operating in a stationary or mobile environment. The receiver is provided with an AC power port for connection via a power cord to an AC power outlet. The receiver is also provided with a DC power port for connection to a DC power source such as a car battery via the cigarette lighter receptacle or power receptacle. One or both of the ports can be provided with a mechanical, magnetic, electromagnetic, semiconductor, electronic or other type of switch or detector that is actuated when the port is connected to its corresponding power source.
In accordance with still another aspect of the present invention, the receiver can also be provided with a motion sensing device. The motion sensing device can be implemented as a vibration sensor (e.g., for sensing when the receiver is being subjected to vibrations induced by a vehicle engine or contact of the vehicle with a road surface), an encoding compass or heading indicator, an encoding gyroscopic device, a mercury switch device, among other devices.
In accordance with an aspect of the present invention, a satellite receiver is configured to be portable for use within a vehicle, as well as for stationary use. The receiver is provided with a vehicle antenna which can be affixed to a vehicle window, for example. The receiver is also provided with a separate antenna for use when the receiver is stationary. An operating mode determining device can be implemented using a mechanical magnetic, electromagnetic, semiconductor, electronic or other type of switch or detector which is actuated when the stationary antenna is deployed and/or when vehicle antenna is connected to a vehicle antenna port on the receiver.